Fairchild 740L6000 Internal Contamination

Gideon Analytical Labs received four Fairchild 74OL6000 field failed Optocouplers along with three good (virgin green dot) devices in which a comparison could be done. The LSTTL input compatibility is provided by an input integrated circuit, with industry standard logic levels. This input amplifier IC switches a temperature compensated current source driving a high speed 850 nm AlGaAs LED emitter. This integration scheme eliminates CTR degradation over time and temperature. The emitter is optically coupled to an integrated photodetector/high-gain, high-speed output amplifier IC. The TTL compatible output has a totem-pole with a fan-out of 10. The CMOS compatible output has an open collector Schottky clamped transistor that interfaces to any CMOS logic between 4.5 and 15 volts. More information on this part can be seen at http://www.alldatasheet.com/datasheet-pdf/pdf/179405/FAIRCHILD/74OL6000.html. Three of the optocouplers were tested in a circuit (the input voltage on pin 2 could be varied from 0 volts to 2.3 volts) and found the output remained low. One intermittent opto functioned in the test circuit, as did the green dotted optos. There was no electrical difference between this “quasi-failed devices” than a good green dotted opto. Next, the optos were tested for leakage current from pin to pin to establish which side of the opto was causing the problem.

Through a series of testing and experimentation, the input IC was found to have excessive leakage between adjacent wire bonds which rendered the IC as “uncontrollable” in the application. The package was decapsulated to find a fiber connecting wire bond and leakage on the IC die. The contamination remained on the die as well as with the fiber.

Gideon Analytical Labs can save money and find solutions to problems that may affect your relationship with your client. This anomaly was probably a one-time event, however, in class 1000 environments with  ICs approaching the .2 microns and several layers of metal nowadays, reliability is based on what is not seen as much as what is seen. Call Gideon Analytical Labs with your next failure analysis.